I have just received my 50 plate chiller from kegcowboy but the sticker on the top has been almost completely worn off. Before I use this I would like to figure out which wort line to use in order to go against the ridges.

There is an arrow type marking on one of the ports as pictured below. Could someone who has one of these tell me the flow directions please.

Just make sure the wort in is the opposite direction flow as the water in.

I don't think that is sufficient. I once asked John Blichmann whether I could reverse the direction of both fluids on the Therminator (I think it has 40 plates), and he said no, the flow patterns are designed to work in only one direction. The chilling efficiency goes way down when the directions are reversed.

Answered a couple posts up. As per the manufacturer, dudadiesel, there is absolutely no difference in performance with direction of flow as long as the wort and water flow opposite. The ridges don't matter.

I swap which one is the wort channel every brew as an extra means of cleaning.